Characterization of monoclonal antibodies directed to canine T lymphocyte markers expressed during development

Two monoclonal antibodies (mAb) which recognize cell surface antigens of canine T lymphocytes are described. mAb RQ1 (of IgG1 subclass) binds a 34 kDa peptide under non-reducing conditions which is expressed, on average, by 27±9% (n = 11 dogs) of thymocytes, with preferential binding for medullary, but not cortical thymocytes. RQ1 adheres to splenic periarteriolar lymphoid sheath cells. In adult dogs (n = 7) RQ1 binds on average 86 ± 7% of unstimulated canine peripheral blood mononuclear cells (CPBMC), 69 ± 13% (n = 11) of lymph node cells, and ≤ 19% (n = 2) of bone marrow cells. RQ1 does not bind canine granulocytes, erythrocytes, fibroblasts or kidney epithelial cells. The relative density of RQ1-binding antigen (expressed as fluorescence intensity per cell) was up to 83% greater in lymph node cells than in thymocytes. Thus, RQ1 appears to preferentially bind mature T cells. In contrast, mAb LQ1 (of IgG3 subclass, which binds a 32 kDa sialic acid containing glycoprotein) recognizes both cortical and medullary canine thymocytes as well as 75± 6% CPBMC. This profile is characteristic of a pan-T cell marker. The simultaneous utilization of these two markers allows for the characterization of canine T lymphocyte development: early lymphocyte (e.g. LQ1 +, RQ1 − thymocytes), common lymphocyte (e.g. LQ1 +, RQ1 + [dim fluorescence] thymocytes), and mature lymphocyte (e.g. LQ1 +, RQ1 + [bright fluorescence]).